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Optimering av bildkvaliteten för SPECT-undersökningar med 111In-Octreoscan vid Norrlands universitetssjukhus: -en Monte Carlo studie
Umeå University, Faculty of Medicine, Department of Radiation Sciences. Umeå University, Faculty of Science and Technology, Department of Physics.
2011 (Swedish)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [sv]

Inom nuklearmedicinsk diagnostik används radioaktiva läkemedel för att utvärdera olika organs metabolism och fysiologiska beteende. Genom att använda en scintillationskamera kan strålningen som erhålls när det administrerade läkemedlet sönderfaller i kroppen detekteras och en funktionell bild över aktivitetsfördelningen erhålls. En tredimensionell bildvolym kan erhållas om gammakameran får rotera runt patienten vilket kallas SPECT (Single Photon Emission Computed Tomography). Bildernas kvalitet är av stor betydelse för att kunna göra en noggrann bedömning av olika patologiska tillstånd. Kvaliteten begränsas av en mängd faktorer och en av dem är Comptonspridda fotoner.

I denna studie optimerades bildkvaliteten för SPECT-undersökningar med 111In-Octreoscan för ett Infinia Hawkeye 4 (GE Healthcare, Wisconsin, USA) SPECT-system vid Norrlands universitetssjukhus (NUS). Optimeringen gjordes med avseende på detektion av små tumörer vid visuell inspektion av 111In-Octreoscan-bilder. Monte Carlo simuleringar användes för att utvärdera tre olika parallellhålskollimatorer med fyra olika fönsterinställningar. Rekonstruktion av bilder gjordes med den iterativa tekniken OSEM (Ordered Subset Expectation Maximization) med olika antal iterationer. Bilderna postfiltrerades med två olika filter med tre kritiska frekvenser vardera.

Den lämpligaste inställningen för NUS visade sig vara MEGP-kollimatorn (Medium Energy General Purpose) tillsammans med en fönsterinställning med två huvudfönster centrerade kring 171 respektive 245 keV utan spridningskorrektion. Mest optimal rekonstruktion visade sig vara med två OSEM-iterationer (10 subsets) och postfiltrering med ett Butterworth-filter med kritisk frekvens 0.40 cm-1 och powerfaktor 8. I övrigt visade sig ELEGP-kollimatorn (Extended Low Energy General Purpose) vara den kollimator som optimerar bildkvaliteten mest med avseende på detektion av små tumörer, men den finns ännu inte på NUS.

Abstract [en]

Optimization of image quality for SPECT imaging with 111In-Octreoscan at the University Hospital of Umeå – a Monte Carlo study

In nuclear medicine diagnostics, radiopharmaceuticals are used for evaluating metabolism and physiological behavior of various organs. By using a scintillation camera, radiation can be detected when the administered drug decays in the body, and the result is a functional image of the activity distribution within the patient. A three-dimensional image volume can be obtained by letting the gamma camera rotate around the patient. This method is called SPECT (Single Photon Emission Computed Tomography). Image quality is very important to make an accurate assessment of various pathological conditions. The quality is limited by many factors and one of them is the Compton scattered photons.

In this study image quality of SPECT-examinations with 111In-Octreoscan were optimized for an Infinia Hawkeye 4 (GE Healthcare, Wisconsin, USA) SPECT-system at the University Hospital of Umeå (NUS). The optimization was made with respect to detecting small tumors for visual inspection of 111In-Octreoscan images. Monte Carlo simulations were used to evaluate three different parallel hole collimators with four different window settings. Reconstruction of images was performed with the iterative technique OSEM (Ordered Subset Expectation Maximization) with different numbers of iterations. The images were post-filtered with two different filters with three critical frequencies each.

The most appropriate setting for the SPECT-system at NUS is the MEGP-collimator (Medium Energy General Purpose) with a window setting of two main windows centered around 171 and 245 keV, without scatter correction. The most optimal reconstruction is obtained by using two OSEM-iterations (10 subsets) and post-filtering with a Butterworth-filter with critical frequency 0.40 cm-1 and power factor 8. The ELEGP-collimator (Extended Low Energy General Purpose) proved however to be the most optimal collimator for detecting small tumors, but this collimator is currently not available at NUS.

Place, publisher, year, edition, pages
2011. , 67 p.
Keyword [sv]
SPECT, gammakamera, Octreoscan, bildkvalitet, OSEM-iteration, kontrast
Identifiers
URN: urn:nbn:se:umu:diva-40260OAI: oai:DiVA.org:umu-40260DiVA: diva2:398950
External cooperation
NUS
Subject / course
Examensarbete i teknisk fysik
Educational program
Master of Science Programme in Engineering Physics
Presentation
2011-01-28, Umeå, 15:00 (Swedish)
Uppsok
Physics, Chemistry, Mathematics
Supervisors
Examiners
Available from: 2011-02-21 Created: 2011-02-21 Last updated: 2012-08-30Bibliographically approved

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